The present invention relates to light emitting diodes, and more particularly, to high-power superluminescent diodes.
High-power superluminescent diodes (SLDS) are useful as low-coherent light sources for optical sensing, fiber-optic gyroscopes, and medical instrumentation, and also as gain media for mode-locked lasers and broad-band tunable lasers. An example of a conventional SLD is shown in FIG. 1. The device 10 includes a body 11 including an active layer 12, an electrode 13, and a narrow stripe 14 of a conductive material. When current is passed between the electrode 13 and the stripe 14, the active layer 12 is activated such that it generates light in the region beneath the stripe 14. The stripe 14 is placed at an angle xcex8 with respect to the sides 15, 16 of the body 11 to minimize feedback within the stripe 14, which causes spectral modulation. Examples of conventional SLDs are provided in U.S. Pat. Nos. 4,821,277, 4,958,355, 4,821,276, 4,793,679, and 4,789,881, each of which is incorporated herein by reference.
The requirements of high-power and single-waveguide-mode operation impose conflicting constraints on the SLD stripe design. For example, output power is increased by increasing the width of the stripe 14. Such an increase in width, however, often results in the conversion to, and support of, multiple transverse modes, thus making the SLD unsuitable for many applications such as coupling to a single-mode optical fiber.
In efforts to increase SLD power while minimizing multiple transverse modes, tapered stripes have been developed as shown in FIG. 2. The tapered stripe design is described, for example, in J. N. Walpole et al., xe2x80x9cHigh-Power Strained-Layer InGaAs/AlGaAs Tapered Traveling Wave Amplifier,xe2x80x9d 61 (7) Appl. Phys. Lett. 740-42 (1992), which is incorporated herein by reference. In the example 20 shown in FIG. 2, the stripe 24 is xe2x80x9ctaperedxe2x80x9d such that the distance between its sides 25, 26 increases as one moves from the side 16 to the side 15 of the body 11. The taper of the stripe 24 collimates light out of the side 15 without causing significant conversion to higher order transverse modes or significant radiation from the sides of the underlying active layer. One potential problem associated with the structure shown in FIG. 2, however, is that the width of the stripe 24 at the body side 15 is relatively large such that it is difficult to couple the device 20 to a single-mode fiber. Furthermore, this wide structure often results in dark-line defects, thus reducing the useful lifetime of the device 20.
The present invention provides light emitting diodes each comprising a body of semiconductor material having a first side surface, a second side surface, and a top surface; and a stripe of conductive material over the top surface of the body. The stripe has a first segment and a second segment, each extending from the first side surface to the second side surface of the body. The width of the stripe is therefore defined by the distance between these two segments. The first and second segments of the stripe are configured such that they are substantially non-parallel, and the width of the stripe at its ends is less than the width of the stripe intermediate its ends.
One advantage of the present invention is that, when configured at an angle with respect to the end faces, it provides superluminescent diodes of high output power.
Another advantage of the present invention is that it provides superluminescent diodes characterized by broad output spectra without significant spectral modulation.
Another advantage of the present invention is that it provides superluminescent diodes that minimize higher order transverse modes.
Another advantage of the present invention is that it provides a high power optical amplifier.
Another advantage of the present invention is that it can be configured as a high power laser by providing external feedback.
Yet another advantage of the present invention is that it provides superluminescent diodes of high output power that are amenable to coupling to single-mode fibers.